The present invention generally relates to an apparatus for recording/reproducing or transmitting/receiving a PCM (pulse code modulation) signal, and particularly relates to a PCM data generating/reproducing circuit applicable to digital data different from each other in recording rate or in transmission rate.
As the apparatus for recording/reproducing a PCM audio signal on/from a magnetic tape, for example, digital audio tape recorders (DATs) are known. The DATs and another group of R-DATs use rotary heads. Standardization of the R-DATs is stated in "DIGITAL AUDIO TAPERECORDER SYSTEM", The DAT Conference, c/o Electronic Industries Association of Japan, June 1987. In a DAT, the sampling frequency is fundamentally set to 48 kHz, that is, a 48k-mode. A 44k-mode having a sampling frequency of 44.1 kHz and a 32k-mode having a sampling frequency of 32 kHz are used other than the 48k-mode. The frame format of a recording signal is formed on the basis of the 48k-mode, and the other 44k- and 32k-modes apply correspondingly to the 48k-mode. Compared with the 48k-mode, the 32k-mode has an idle data area portion because data for the 32k-mode are stored in its data area having a capacity for the 48k-mode in spite of the fact that the 32k-mode has an amount of information per unit time which is smaller than that of the 48k-mode. The data area of the frame format has data addresses from 0 to 1455 and the data addresses from 0 to 1439 are efficiently used in the 48k-mode. In the 32k-mode, however, only the data addresses from 0 to 959 are used. If comparison is made as to redundancy (in the above-mentioned document, page 47), the redundancy is 58.3% in the 32k-mode, while 37.5% in the 48k-mode.
Further, with respect to the DATs, no protocol has been defined concerning the processing of two modes different from each other in amount of information, that is, 16-bit linear recording and 16-12 compression non-linear recording in the same 48 kHz sampling 2 channels.
Accordingly, there has been a problem in that, if data of the 32k-mode in which the amount of information is smaller than that in the 48k-mode are entered into a PCM signal generating device set to the 48k-mode to thereby generate a PCM signal having a signal format common to that of the 48k-mode, the redundancy of the generated PCM signal becomes unnecessarily high.